In known types of semiconductor device, adjusting voltage applied to the gate region changes resistance between the emitter region and the collector region or between the source region and the drain region. For example, in the case of an IGBT device, the application of voltage to the gate region reduces resistance between the emitter and the collector, resulting in current flowing between the emitter and the collector. In the case of a MOS device, the application of voltage to the gate region reduces resistance between the source and the drain, resulting in current flowing between the source and the drain. The gate region as used in the present specification may be referred to as a base region.
A semiconductor device of the types described above may be included in an inverter that controls current passing through a motor. Such an inverter includes a parallel circuit including series circuits connected in parallel, with each series circuit including an upper-row semiconductor device and a lower-row semiconductor device connected in series. In this case, an abnormality, for example, a short circuit of a coil in the motor, may result in an excess current flowing through the semiconductor devices. When the operation of the inverter is normal, an upper-row semiconductor device and a lower-row semiconductor device do not turn on simultaneously. If however, an abnormality that causes both of them to turn on simultaneously occurs, an excess current flows through the semiconductor devices.
If an abnormality of any kind occurs to cause an excess current to flow through a semiconductor device, the semiconductor device experiences a rise in temperature. There is a demand for a technique to protect a semiconductor device from overheating. In an attempt to meet the demand, techniques to protect a semiconductor device from overheating through heat dissipation or cooling have been developed, and a technique in Patent Document 1 has been developed.
The technique in Patent Document 1 joins a lead frame or a bus bar to a surface electrode formed on the surface of a semiconductor device. It is expected that such a structure allows heat produced in the semiconductor device to be transferred through the surface electrode to the lead frame or the like to thereby protect the semiconductor device from overheating.